During fuel cell operation, byproducts such as product water and nitrogen, and unconsumed hydrogen may form at the anode side of a fuel cell stack. In certain known systems, accumulation of product water and nitrogen accumulation is controlled in an attempt to avoid a reduction in fuel cell performance, and/or fuel cell system shut down. One known approach is to release the water and nitrogen via a passageway downstream of the fuel cell stack. The byproducts may be recirculated such that the unconsumed hydrogen is returned to the anode side of the fuel cell stack. Also, recirculation may be used to humidify the anode side to promote efficient chemical conversion and extend cell membrane life. However, liquid water in the recirculation stream, such as droplets, may need to be removed to prevent water blockages within fuel cell stack flow field channels or an ejector.
Traditional water separators have flow paths, screens and/or meshes that entrain water droplets in flow impact for water removal. These devices may have high water removal efficiencies, e.g., up to 99%. However, the design of these conventional devices causes a relatively large pressure drop across the system for a given volume of the device.
For an ejector based fuel cell system with a passive recirculation loop, minimizing the pressure drop through an anode loop of a fuel cell system may be critical. Ejectors are momentum transfer devices, and as such, the passive recirculation flow they induce is a function of compression work performed by the ejector. Any pressure drops within the anode loop increase the compression work for the ejector, and may limit the recirculation flow. The dominant pressure drop in the anode loop is caused by the fuel cell stack, and pressure drops across other components, such as a water separator, need to be minimized for the ejector and fuel cell to function properly. Additionally, the high efficiency of conventional separators may result in too low of humidity and degrade fuel cell performance and life as some humidity is desirable in the recirculation flow.